Currently, it is considered that many food fibers which are not digestive promote the excretion of sodium ion, and serve to excrete toxic substances. These functions of food fibers are primarily attributed to (1) the ion exchange capacity thereof, and (2) the swellability (water retention) thereof. Many food fibers have an ion exchange capacity of about 0.1-0.4 meq/g (Nihon-Kaseigakukai-Si 39, 187-195(1988)), and thus, for an adsorption of sodium corresponding to 1 g of sodium chloride, it is necessary to ingest 40-200 g (dry weight) of food fibers; it is difficult, however, in everyday life, to ingest such an amount of food fibers. Regarding the swellability (water retention) thereof, agar can absorb and retain an amount of about four times the dry weight of a solution, alginic acid can absorb and retain an amount of about four to five times the dry weight of the solution, and wheat bran can absorb and retain an amount of about four times the dry weight of the solution. One gram of such food fibers can retain about 4 g of humor (liquor in the cavity of the digestive tract), which contains an amount of sodium corresponding to about 30 mg of sodium chloride. Therefore, to excrete 1 g of sodium chloride, it is necessary to ingest 30 to 40 g of food fibers, and although such an ingestion is not impossible, it is difficult to continue for a long time.